1. Field of the Invention
The present invention relates to a power supply circuit.
2. Description of the Related Art
In an AC-DC converter, a target level DC voltage is generated when a transistor to which a voltage according to an AC voltage is applied is switched in general. Also, as a Power Factor Correction (PFC) control method in the AC-DC converter, a partial switching method is known as a method of using an inductor which is inexpensive but poor in frequency characteristics (silicon steel plate reactor, for example) (Japanese Patent Laid-Open No. 2000-224858, for example).
In the partial switching method, switching of the transistor is stopped in the vicinity of a peak of an AC voltage inputted to the AC-DC converter. Then, a zero-cross detection circuit and a microcomputer are required for the AC-DC converter to execute the partial switching method.